Should i change my Crank set for more speed

cheaperholidays

Hi all my sirrus has 48 x 38 x 28T would anyone reccomend a road crankest to replace this.

I am currently averaging just over 15mph for 4 hour runs on my own, not part of a chain, but i would like to complete a 100 mile event in 6 hours around the cotswolds

danowat

Depends what is the limiting factor to your speed, is it.....

1) Gearing
2) Fitness
3) Cadence

Fitting higher gearing won't automatically make you faster

edit : I reckon its either 2 or 3 that is the limiting factor, rather than the gearing.

The Sirrus has a higest gear of 48-12, which at a maintainable cadence of 80rpm, gives you 25.2mph, which is plenty of speed, I'd work on your fitness and/or cadence before chucking money at the issue

cheaperholidays

danowat wrote:

Depends what is the limiting factor to your speed, is it.....

1) Gearing
2) Fitness
3) Cadence

Fitting higher gearing won't automatically make you faster

edit : I reckon its either 2 or 3 that is the limiting factor, rather than the gearing.

The Sirrus has a higest gear of 48-12, which at a maintainable cadence of 80rpm, gives you 25.2mph, which is plenty of speed, I'd work on your fitness and/or cadence before chucking money at the issue

I would like to see someone push that gear at 80rpm unless there going downhill

emx

cheaperholidays wrote:

I would like to see someone push that gear at 80rpm unless there going downhill

so you don't need a new chainset then..?

danowat

emx wrote:

cheaperholidays wrote:

I would like to see someone push that gear at 80rpm unless there going downhill

so you don't need a new chainset then..?

Exactly!!!

If you can't push 48-12, what on earth makes you think you'll be able to push a harder gear!!

cheaperholidays

I can spin at 90 to 100 rpm in the 5th gear which puts the chain in line with the large chain ring, but the ratios seem far apart if you change to the 4th gear you start to spin too fast and 6th gear your grinding.

If you see what i mean

emx

so you want closer ratios - not 'more speed'.

danowat

5th gear on a 9sp 12-25 block is 17T, 90-100rpm in said gear (48-17) is 20-22.3mph

Ergo, if you can maintain 90-100rpm in 5th, then you should be able to maintain at least 20mph.

6th gear on said block is 15T, if you can't push the next one down, then you need to work on your body, changing gears won't help.

cheaperholidays

The rear cassette is an 8-speed, 11-32t 11,13,15,18,21,24,28,32
if i was to change the rear i would like to keep 3 lowest gears and change the ratios of the remaining 5 to more road bike gears.

So in 5th i am pushing 48 - 18 and 48 - 15 in 6th not sure how you work out the potential mph at 90 to 100 rpm.

Is this possible can your lbs get the gears and put them together?

Edit i can spin in 6th 48 - 15 bit it feels wrong and i can go faster when spinning 48 -18 so should i concentrate on spinning up the 48 - 15 ratio?

johnmiosh

Try the rabbit gear calculator. It is a flash application to download free.
http://software.bareknucklebrigade.com/

johnmiosh

Sorry, Java not flash

Mike67

Maybe something like the Shimano HG50 12-23 or 12-25
[/url]http://www.ukbikestore.co.uk/product/17/cshg508_rd/shimano-sora-hg50-8-speed-road-cassette.html

or SRAM PG850 12-23 or 12-26

http://www.wiggle.co.uk/sram-pg850-8-speed-cassette/[url]

Would be more what you're after to get less of a step change. Three of them step down from 17 to 15 to 14 as detailed here:

[/url]http://sheldonbrown.com/k8.shtml[url][/url]

Mike67

Mmm links don't seem to have worked there

Mike67

http://sheldonbrown.com/k8.shtml
http://www.ukbikestore.co.uk/product/17/cshg508_rd/shimano-sora-hg50-8-speed-road-cassette.html
http://www.wiggle.co.uk/sram-pg850-8-speed-cassette/

Hopefully working now

dulldave

You're changing a flat barred commuter to a drop handlebar set up. That's quite expensive. It also seems you want closer ratios more like a road bike.

What you want is a drop handlebar road bike.

You'll end up wanting to change something else about it before long (the geometry might be a bit weird for example) and when you finally get round to buying a road bike you'll be trying to sell a commuter that's been turned into a road bike = not a lot of interested buyers.

You're better off selling it as a commuter to someone who wants a commuter and then getting yourself a secondhand road bike.

cheaperholidays

The sirrus is the specialized Allez with flat bars apparently, but i see your point dulldave

freehub

cheaperholidays wrote:

danowat wrote:

Depends what is the limiting factor to your speed, is it.....

1) Gearing
2) Fitness
3) Cadence

Fitting higher gearing won't automatically make you faster

edit : I reckon its either 2 or 3 that is the limiting factor, rather than the gearing.

The Sirrus has a higest gear of 48-12, which at a maintainable cadence of 80rpm, gives you 25.2mph, which is plenty of speed, I'd work on your fitness and/or cadence before chucking money at the issue

I would like to see someone push that gear at 80rpm unless there going downhill

I don't understand, plenty of people could do that.

2alexcoo

cheaperholidays wrote:

The sirrus is the specialized Allez with flat bars apparently, but i see your point dulldave

Looking at the geometry tables, the Sirrus has a much slacker head angle, more fork rake, a taller head tube, much longer chainstays and numerous other differences to the Allez.

They're different bikes for different types of riding.

SBezza

freehub wrote:

cheaperholidays wrote:

danowat wrote:

Depends what is the limiting factor to your speed, is it.....

1) Gearing
2) Fitness
3) Cadence

Fitting higher gearing won't automatically make you faster

edit : I reckon its either 2 or 3 that is the limiting factor, rather than the gearing.

The Sirrus has a higest gear of 48-12, which at a maintainable cadence of 80rpm, gives you 25.2mph, which is plenty of speed, I'd work on your fitness and/or cadence before chucking money at the issue

I would like to see someone push that gear at 80rpm unless there going downhill

I don't understand, plenty of people could do that.

+1 to that, if you are fit enough, and powerful enough it is easy to do. Just work on it, and you will get faster as you get fitter.

cheaperholidays

"freehub wrote:

I don't understand, plenty of people could do that.

I thought the idea was to spin up and not grind, since i live in wales and nowhere is realy flat, trying spin in that gear would blow my legs up...

SBezza

Cadence is a personal thing, I normally ride around 80-90 rpm, and it is not grinding. On the turbo I usually go over 100 rpm however. You should be able to ride comfortably over a range of cadences, as you need different cadences for different terrain.

Some people ride at 25mph + on the flats so at 48x12 80+ rpm would be normal for some riders.

cheaperholidays

SBezza wrote:

Cadence is a personal thing, I normally ride around 80-90 rpm, and it is not grinding. On the turbo I usually go over 100 rpm however. You should be able to ride comfortably over a range of cadences, as you need different cadences for different terrain.

Some people ride at 25mph + on the flats so at 48x12 80+ rpm would be normal for some riders.

Thanks Sbezza now i get the point, i think i misunderstood the whole spinning thing, will give it a go next week..

brettjmcc

cheaperholidays wrote:

I am currently averaging just over 15mph for 4 hour runs on my own, not part of a chain, but i would like to complete a 100 mile event in 6 hours around the cotswolds

I did my first centurary last year. I trained solo, and I managed 73 miles in just over 4 hours on one very hard training run on similar terrain. On the day of the event I ended up doing it in just over 6 hours covering 103 miles (though getting into a childish drinking contest 2 weeks before knocked my trainign way out).

I'd look to try to also push your training routes up in your average speed a bit, though working with people on the event will also make it easier for you.

I think you are down in South Wales, right? My wife's parents live up Ystrad Mynach way if you ever fancy a ride when we go down there one weekend let me know. Also, she got 'Facebooked' by an old school friend who still lives in Blackwood - only turns out he's the Olypic Development Coach for British Cycling! He's promised to go out for a ride with me (when it warmer of course - I don't do this freeze my butt off, but I also actually like turbos....)

Brett

cheaperholidays

Hi Brett, thanks for the invite that would be superb, part of my training also involves going up and over the Rhigos and Bwlch as part of a 60 mile loop.

I intend to up the cadence on the higher gears on my next run , but wales is not flat so on a 60 mile flat run i would go off like billy wizz lol

brettjmcc

LOL, if you're doing that kind of speed over Bwlch, I'll borrow your Blade.... Still I might be back to that kind of fitness by summer

vinnn

Hi, sorry but I think Dulldave hit the nail on the head.
There's a few hints here that you're trying to convert a hybrid into a road bike to gain some road bike performance.

My opinion is that such a thing won't work as your Spesh Sirrus is not a road bike and is not the same as a Spesh Allez.
The Sirrus' frame geometry allows for a more upright riding position at the front and slacker seat tube angle, even with drops and a change of stem your riding position is unlikely to be the same as your average road bike.
Your Sirrus' gear sizing will be different front & back than your average road bike too, also the chainset isn't likely to have the same q factor or stiffness than a dedicated road chainset.
The Sirrus is also fitted with V-Brakes, not calipers which will likely prevent you from putting road brake levers on the drops unless you also fit calipers and plug up the V-Brake pivot mounts in your frame & forks.

As Dulldave suggests, once you've spent money trying to convert your Sirrus to a drop-bar bike with road gearing and all the extra bits that'd need to be changed you would've likely spent almost enough to pay for a cheap road bike and you'll still be wanting to change more.
Keep your Sirrus the way it is and buy a road bike or sell the Sirrus to fund one.


Aside from that if you simply want to close those gaps between your gear ratios just buy a new cassette with a closer range such as 12-25.

Hope that helps...